Electrochemical detection is attractive because it provides high sensitivity, small dimensions, low cost, fast response, and compatibility with microfabrication technologies. These characteristics have led to the development of a variety of sensors based on amperometric, potentiometric or impedimetric signals and their assembly into arrays for chemical, biochemical and cellular applications. In particular, several of these developments involve the use of large-scale arrays of electrochemical sensors for monitoring multiple reaction steps on a large plurality of analytes confined to such an array. Typically in such systems, analytes are randomly distributed among an array of confinement regions, such as microwells or reaction chambers, and reagents are delivered to such regions by a fluidics system that directs flows of reagents through a flow cell containing the sensor array. Microwells in which reactions take place, as well as empty wells where no reactions take place, may be monitored by one or more electronic sensors associated with each of the microwells.
Such systems are subject to a host of interrelated phenomena that make highly sensitive measurements challenging, particularly under low signal conditions. Such phenomena include unstable reference voltage for the electrical sensors, lack of knowledge as to which confinement regions contain analytes, variability in the amount of reagents delivered by a flow stream to analytes confined to different regions of an array, potential mixing of successively delivered reagents, changes in instrument temperature, fluid leaks that may affect fluid potential, extraneous electrical interference, e.g. 60 Hz noise, cell phones, or the like, all of which may affect the quality of signals collected. In addition, “decoding” signals and relating them to identification and quantification of analytes subject to interrogation by the electrochemical detection system presents challenges in terms of throughput, precision, and accuracy.
In view of the above, it would be advantageous to have available a system for carrying out multi-reagent electrochemical reactions in parallel on a large number of analytes which overcame the deficiencies of current approaches.